The present invention relates to a new and improved method of improving the operation of backwashable fixed beds formed of granular materials and which are typically employed during the purification of waste water of sewage or during water treatment. Examples of the aforementioned fixed beds are, for instance, sand filters, activated carbon-adsorbers and ion exchangers.
In the context of the disclosure of this invention, the term "backwashing" or "backflushing", when used and where appropriate, is employed in its broader sense to embrace not only flow of the flushing liquid counter-current to the treated liquid but also substantially in the same direction of flow thereof.